Dendritic cell-derived hepcidin sequesters iron from the microbiota to promote mucosal healing.

Bleeding and altered iron distribution occur in multiple gastrointestinal diseases, but the importance and regulation of these changes remain unclear. We found that hepcidin, the master regulator of systemic iron homeostasis, is required for tissue repair in the mouse intestine after experimental damage. This effect was independent of hepatocyte-derived hepcidin or systemic iron levels. Rather, we identified conventional dendritic cells (cDCs) as a source of hepcidin that is induced by microbial stimulation in mice, prominent in the inflamed intestine of humans, and essential for tissue repair. cDC-derived hepcidin acted on ferroportin-expressing phagocytes to promote local iron sequestration, which regulated the microbiota and consequently facilitated intestinal repair. Collectively, these results identify a pathway whereby cDC-derived hepcidin promotes mucosal healing in the intestine through means of nutritional immunity.

Targeting mitochondrial RNA polymerase in acute myeloid leukemia.

Acute myeloid leukemia (AML) cells have high oxidative phosphorylation and mitochondrial mass and low respiratory chain spare reserve capacity. We reasoned that targeting the mitochondrial RNA polymerase (POLRMT), which indirectly controls oxidative phosphorylation, represents a therapeutic strategy for AML. POLRMT-knockdown OCI-AML2 cells exhibited decreased mitochondrial gene expression, decreased levels of assembled complex I, decreased levels of mitochondrially-encoded Cox-II and decreased oxidative phosphorylation. POLRMT-knockdown cells exhibited an increase in complex II of the electron transport chain, a complex comprised entirely of subunits encoded by nuclear genes, and POLRMT-knockdown cells were resistant to a complex II inhibitor theonyltrifluoroacetone. POLRMT-knockdown cells showed a prominent increase in cell death. Treatment of OCI-AML2 cells with 10-50 µM 2-C-methyladenosine (2-CM), a chain terminator of mitochondrial transcription, reduced mitochondrial gene expression and oxidative phosphorylation, and increased cell death in a concentration-dependent manner. Treatment of normal human hematopoietic cells with 2-CM at concentrations of up to 100 µMdid not alter clonogenic growth, suggesting a therapeutic window. In an OCI-AML2 xenograft model, treatment with 2-CM (70 mg/kg, i.p., daily) decreased the volume and mass of tumours to half that of vehicle controls. 2-CM did not cause toxicity to major organs. Overall, our results in a preclinical model contribute to the functional validation of the utility of targeting the mitochondrial RNA polymerase as a therapeutic strategy for AML.

The interaction of protein-tyrosine phosphatase α (PTPα) and RACK1 protein enables insulin-like growth factor 1 (IGF-1)-stimulated Abl-dependent and -independent tyrosine phosphorylation of PTPα.

Protein tyrosine phosphatase α (PTPα) promotes integrin-stimulated cell migration in part through the role of Src-phosphorylated PTPα-Tyr(P)-789 in recruiting and localizing p130Cas to focal adhesions. The growth factor IGF-1 also stimulates PTPα-Tyr-789 phosphorylation to positively regulate cell movement. This is in contrast to integrin-induced PTPα phosphorylation, that induced by IGF-1 can occur in cells lacking Src family kinases (SFKs), indicating that an unknown kinase distinct from SFKs can target PTPα. We show that this IGF-1-stimulated tyrosine kinase is Abl. We found that PTPα binds to the scaffold protein RACK1 and that RACK1 coordinates the IGF-1 receptor, PTPα, and Abl in a complex to enable IGF-1-stimulated and Abl-dependent PTPα-Tyr-789 phosphorylation. In cells expressing SFKs, IGF-1-stimulated phosphorylation of PTPα is mediated by RACK1 but is Abl-independent. Furthermore, expressing the SFKs Src and Fyn in SFK-deficient cells switches IGF-1-induced PTPα phosphorylation to occur in an Abl-independent manner, suggesting that SFK activity dominantly regulates IGF-1/IGF-1 receptor signaling to PTPα. RACK1 is a molecular scaffold that integrates growth factor and integrin signaling, and our identification of PTPα as a RACK1 binding protein suggests that RACK1 may coordinate PTPα-Tyr-789 phosphorylation in these signaling networks to promote cell migration.

Alveolar macrophages and neutrophils are the primary reservoirs for Legionella pneumophila and mediate cytosolic surveillance of type IV secretion.

Legionella pneumophila, an intracellular pathogen responsible for the severe pneumonia Legionnaires' disease, uses its dot/icm-encoded type IV secretion system (T4SS) to translocate effector proteins that promote its survival and replication into the host cell cytosol. However, by introducing bacterial products into the host cytosol, L. pneumophila also activates cytosolic immunosurveillance pathways, thereby triggering robust proinflammatory responses that mediate the control of infection. Thus, the pulmonary cell types that L. pneumophila infects not only may act as an intracellular niche that facilitates its pathogenesis but also may contribute to the immune response against L. pneumophila. The identity of these host cells remains poorly understood. Here, we developed a strain of L. pneumophila producing a fusion protein consisting of ß-lactamase fused to the T4SS-translocated effector RalF, which allowed us to track cells injected by the T4SS. Our data reveal that alveolar macrophages and neutrophils both are the primary recipients of T4SS-translocated effectors and harbor viable L. pneumophila during pulmonary infection of mice. Moreover, both alveolar macrophages and neutrophils from infected mice produced tumor necrosis factor and interleukin-1α in response to T4SS-sufficient, but not T4SS-deficient, L. pneumophila. Collectively, our data suggest that alveolar macrophages and neutrophils are both an intracellular reservoir for L. pneumophila and a source of proinflammatory cytokines that contribute to the host immune response against L. pneumophila during pulmonary infection.

Caspase-11 activation in response to bacterial secretion systems that access the host cytosol.

Inflammasome activation is important for antimicrobial defense because it induces cell death and regulates the secretion of IL-1 family cytokines, which play a critical role in inflammatory responses. The inflammasome activates caspase-1 to process and secrete IL-1ß. However, the mechanisms governing IL-1α release are less clear. Recently, a non-canonical inflammasome was described that activates caspase-11 and mediates pyroptosis and release of IL-1α and IL-1ß. Caspase-11 activation in response to Gram-negative bacteria requires Toll-like receptor 4 (TLR4) and TIR-domain-containing adaptor-inducing interferon-ß (TRIF)-dependent interferon production. Whether additional bacterial signals trigger caspase-11 activation is unknown. Many bacterial pathogens use specialized secretion systems to translocate effector proteins into the cytosol of host cells. These secretion systems can also deliver flagellin into the cytosol, which triggers caspase-1 activation and pyroptosis. However, even in the absence of flagellin, these secretion systems induce inflammasome activation and the release of IL-1α and IL-1ß, but the inflammasome pathways that mediate this response are unclear. We observe rapid IL-1α and IL-1ß release and cell death in response to the type IV or type III secretion systems of Legionella pneumophila and Yersinia pseudotuberculosis. Unlike IL-1ß, IL-1α secretion does not require caspase-1. Instead, caspase-11 activation is required for both IL-1α secretion and cell death in response to the activity of these secretion systems. Interestingly, whereas caspase-11 promotes IL-1ß release in response to the type IV secretion system through the NLRP3/ASC inflammasome, caspase-11-dependent release of IL-1α is independent of both the NAIP5/NLRC4 and NLRP3/ASC inflammasomes as well as TRIF and type I interferon signaling. Furthermore, we find both overlapping and non-redundant roles for IL-1α and IL-1ß in mediating neutrophil recruitment and bacterial clearance in response to pulmonary infection by L. pneumophila. Our findings demonstrate that virulent, but not avirulent, bacteria trigger a rapid caspase-11-dependent innate immune response important for host defense.

Innate lymphoid cells promote anatomical containment of lymphoid-resident commensal bacteria.

The mammalian intestinal tract is colonized by trillions of beneficial commensal bacteria that are anatomically restricted to specific niches. However, the mechanisms that regulate anatomical containment remain unclear. Here, we show that interleukin-22 (IL-22)-producing innate lymphoid cells (ILCs) are present in intestinal tissues of healthy mammals. Depletion of ILCs resulted in peripheral dissemination of commensal bacteria and systemic inflammation, which was prevented by administration of IL-22. Disseminating bacteria were identified as Alcaligenes species originating from host lymphoid tissues. Alcaligenes was sufficient to promote systemic inflammation after ILC depletion in mice, and Alcaligenes-specific systemic immune responses were associated with Crohn's disease and progressive hepatitis C virus infection in patients. Collectively, these data indicate that ILCs regulate selective containment of lymphoid-resident bacteria to prevent systemic inflammation associated with chronic diseases.

Pyogenic liver abscess: an audit of 10 years' experience.

AIM: To describe our own experience with pyogenic liver abscesses over the past 10 years and investigate the risk factors associated with failure of initial percutaneous therapy. METHODS: A retrospective study of records of 63 PLA patients presenting between 1998 and 2008 to Australian tertiary referral centre, were reviewed. Amoebic and hydatid abscesses were excluded. Demographic, clinical, radiological, and microbiological characteristics, as well as surgical/radiological interventions, were recorded. RESULTS: Sixty-three patients (42 males, 21 females) aged 65 (± 14) years [mean ± (SD)] had prodromal symptoms for a median (interquartile range; IQR) of 7 (5-14) d. Only 59% of patients were febrile at presentation; however, the serum C-reactive protein was elevated in all 47 in whom it was measured. Liver function tests were non-specifically abnormal. 67% of patients had a solitary abscess, while 32% had > 3 abscesses with a median (IQR) diameter of 6.3 (4-9) cm. Causative organisms were: Streptococcus milleri 25%, Klebsiella pneumoniae 21%, and Escherichia coli 16%. A presumptive cryptogenic cause was most common (34%). Four patients died in this series: one from sepsis, two from advanced cancer, and one from acute myocardial infarction. The initial procedure was radiological aspiration ± drainage in 54 and surgery in two patients. 17% underwent surgical management during their hospitalization. Serum hypoalbuminaemia [mean (95% CI): 32 (29-35) g/L vs 28 (25-31) g/L, P = 0.045] on presentation was found to be the only factor related to failure of initial percutaneous therapy on univariate analysis. CONCLUSION: PLA is a diagnostic challenge, because the presentation of this condition is non-specific. Intravenous antibiotics and radiological drainage in the first instance allows resolution of most PLAs; However, a small proportion of patients still require surgical drainage.

Parents' global rating of mental health correlates with SF-36 scores and health services satisfaction.

BACKGROUND: Patient satisfaction surveys are often used to measure quality of care. However, patient satisfaction may not be a reliable indicator of service quality because satisfaction can be influenced by clients' characteristics such as their health status. METHODS: Parents of children attending a pediatric neurology clinic completed the Short Form Health Survey (SF-36) and global ratings of their physical and mental health. They also completed the Client Satisfaction Questionnaire (CSQ), the Measure of Processes of Care (MPOC), and the Family-Centered Care Survey (FCCS). RESULTS: 104 parents completed the survey. The correlation between the global rating of physical or mental health and their corresponding SF-36 scores was high. The majority (88%) of parents were satisfied, with a median CSQ score of 28 (IQR, 24 to 31) and a FCCS score of 4.7 (IQR, 4.2 to 4.9). Logistic regression identified parents' mental health as a significant predictor of client satisfaction (OR, 1.07; 95% CI, 1.01 to 1.14). CONCLUSIONS: Given the positive association between parents' mental health and satisfaction with care, it is important to consider mental status as a covariate in interpreting satisfaction surveys. Parents' global rating of mental health appears to be a reasonable indicator of their SF-36 mental scores.